Plain text files saved from ClarisWorks 2.0 are saved as MacWrite 5.0 text files (the file Type attribute is MACA). Therefore, if you save from ClarisWorks 2.0 as a plain text file, then try to reopen it into ClarisWorks by double-clicking the text file icon, you'll see an alert that says "The document XXX could not be opened because the document that created it could not be found."
To open the file:
1- Use the Open command in the ClarisWorks File Menu (Be sure to choose "Word Processing" as the Document Type in the "Open" dialog box), or
2- Drop-launch the file icon onto the ClarisWorks application icon (drag the icon onto the ClarisWorks application icon {not a folder icon}, then release the mouse button).